Slime On Surface?

So I noticed a month after moving into a new house that my single Betta tank had gotten a slime like substance along the top of the water and that when I shone I light on it, it was rainbow colored. I read a couple of articles that it's a bacteria biofilm? So I completely cleaned the tank, baked the rocks, used a touch of bleach to soak the aquarium and all the accessories that wouldn't absorb the bleach water.
It has been a week and the rainbow slime is slowly coming back.
I would hate to have to stress Balerion out by performing another deep cleaning, and I'm hoping someone can give me some help?
Our house is very humid and he stays in the kitchen (where we don't cook a lot, especially since I cleaned his tank).
There are two windows in the room but it generally doesn't get much sunlight.
I've had balerion for almost two years, please help me round it out, he's a delightful little man and I would hate to lose him

 

Its a protien film and is normal adding surface aggitation or a surface skimmer will break it up otherwise its always going to be there.

 

Its a protien film and is normal adding surface aggitation or a surface skimmer will break it up otherwise its always going to be there.

It's usually caused by food waste and their waste. but +1

 

It's usually caused by food waste and their waste. but +1

The protien in the food is one source.

 

What kind of aquarium filter do you use? I wonder what kind of surface agitation you do currently have.

However, instead of surface agitation being an issue, I think it might be more related to the steam that comes from your cooking in the kitchen where the tank is located. Whereas, it could be cooking grease or other foods turning to some kind of steam that some eventually ends up to the aquarium's water surface.

I don't think you need to do another deep cleaning with bleach or heat rocks.